On Tue, Oct 2, 2012 at 5:20 PM, Russ White <[email protected]> wrote: >> - Path information is lost. While this doesn't impact loop prevention, this >> information is operationally useful. I'll offer the counter that this is >> already done today through explicit policy, typically either because the >> operator knows this is safe or because they simply don't care about the >> consequences to forwarding. > > I don't get how path information is lost in this draft. The AS Path is > not altered in any advertisement, so it's not like aggregation, where > you replace a series of AS' with a single AS, or anything like that.
Hi Russ, 10.1.0.0/16 AS path 12 5 4 2 10.1.1.0/24 AS path 12 1 The 12->1 path, 1 being a completely different origin AS than the covering route's origin from 2, is lost when 10.1.1.0/24 is aggregated into 10.1.0.0/16. >> - In several cases, the more specific prefix may be information that is >> *not* present from the originating AS - i.e. a subnet has "wandered away". >> Such situations will become increasingly common as the Internet >> deaggregates under pressure of address space exhaustion. This is my >> primary concern. > > I don't get this one, either... The prior example exhibits this case as well. >> - But even if they do share a common origin AS, if you have an internal AS >> partition, things may be unhappy if the more specific provided you >> forwarding coverage and it got suppressed. > > AS partitions are already handled in the draft as written. If the two > routers with overlapping prefixes aren't reachable through iBGP (no > matter what their AS numbers might happen to me), then the mechanism > won't suppress the longer prefix. Suppose an Internet-connected network consists of site A and site B. 10.1.1.0/24 is advertised from and used by site A while 10.1.2.0/24 is advertised from and used by site site B. Both sites advertise 10.1.0.0/16. Sites A and B are connected to each other, so if site A receives a packet for 10.1.2.1, it will forward it to site B. If site B should lose its internet connection, packets for 10.1.2.1 will follow the covering route via site A and still reach site B. Regardless of aggregation. Instead, lose the connection from site A to site B but keep both sites connected to the Internet. The covering route continues to appear at your router but if you send 10.1.2.1 to site A because you discarded the more specific route, you have black-holed that packet. Even though site B is connected to the Internet. In normal operation, another nasty problem appears. Site A is in London. Site B is in Honolulu. You're in Chicago. Your packet to 10.1.2.1 follows the closest aggregated route to London before it can travel to Honolulu, adding thousands of miles and near a hundred milliseconds to its trip. Regards, Bill Herrin -- William D. Herrin ................ [email protected] [email protected] 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004 _______________________________________________ GROW mailing list [email protected] https://www.ietf.org/mailman/listinfo/grow
